80211 The longest interval between frames is

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• ADIFS

• A
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Explanation

DIFS (Distributed Coordination Function Interframe Space) is the longest of the standard interframe spaces in 802.11, used by stations before transmitting regular data frames under the DCF (Distributed Coordination Function) access method. Its longer duration ensures that high-priority control frames using shorter intervals (SIFS and PIFS) always get channel access first, creating a clear priority hierarchy.

Why distractors are wrong:

• SIFS (Short Interframe Space) is the shortest interval, used for high-priority responses like ACKs and CTS frames to ensure immediate replies without contention.
• PIFS (PCF Interframe Space) sits in the middle of the hierarchy (PIFS = SIFS + 1 slot time), used by the Point Coordination Function for polling in infrastructure mode.
• These shorter gaps guarantee time-sensitive control traffic always wins channel access before regular data.

Memory tip: Think of the hierarchy as a priority ladder - SIFS (Shortest/highest priority) → PIFS (medium) → DIFS (longest wait/lowest priority for regular data). The acronym order S-P-D maps directly to shortest-to-longest, and D for DIFS = "Delay the most."

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